Fire and Ice

by Barbara Eaglesham

Who doesn't love diamonds? They're rare, and forever. They sparkle. They symbolize love.

But…what if they weren't rare? What if they were made in a laboratory using extremely high pressure, and instead of being 3 billion years old, they were made last week? Would they still be as desirable?

Synthetic diamonds are being created in laboratories. And some are being sold as gems. But the vast majority of “created” diamonds will never wind up on a hand or an earlobe. They are being grown with a different purpose in mind: science and technology.

Scientists have been taking advantage of the unique properties of diamonds and experimenting with them in some surprising ways. Someday soon, you may be wearing sunglasses coated with diamond, and looking into a diamond-coated monitor screen that is attached to a computer whose memory is stored on diamond instead of silicon. The sunglasses will be scratch-proof, the screen brighter, the computer more powerful. And they won't cost a bundle, either!

Molecule of the Year

What makes diamond so special that Science magazine named it “Molecule of the Year” in 1990? For one thing, it is the hardest known substance—it can scratch anything and nothing else can scratch it.

German mineralogist Friedrich Mohs devised a scale in the 1800s to rate the hardness of minerals. On this scale, diamond is a 10; at the other extreme is graphite with a rating of less than one. Diamond conducts heat and sound better than any other substance, making the Backstreet Boys sound even better when heard through new, high-tech speakers with diamond membranes. Diamond doesn't conduct electricity well, so it can be used as an insulator. Thin diamond films are often used to protect delicate components in electrical equipment. Diamond is also optically clear and chemically inert at room temperature (it won't break down in the presence of any known chemical). These properties make diamond attractive as a tool for studying the behavior of various substances under very high pressures, and in a host of other applications scientists are only just beginning to dream up.

Carbon Copy

In 1772, the French chemist Antoine-Laurent Lavoisier, dressed in his customary powdered wig and embroidered coat, sealed a diamond in a jar with oxygen. Using a thick glass lens, he focused the sun's heat on the diamond, and then watched as it glowed and burned until it… disappeared! The only thing left was carbon dioxide gas. This experiment proved that diamond is made of pure carbon. Graphite, which fills our pencils, is also made of pure carbon. How can diamond and graphite be made of the same element? One is the hardest mineral known, and the other is so soft that it can be rubbed onto paper.

The answer lies 150 to 200 km below the Earth's surface, in its mantle. Diamonds formed here a few billion years ago under a pressure of 50,000 atmospheres and at temperatures near 1,300 degrees C. Under these conditions, carbon atoms crystallizing out of the molten soup were forced into a densely packed arrangement. Each carbon atom was stable (unchanging) at this elevated temperature and pressure, and bonded to four other carbon atoms as a tetrahedron. The tetrahedrons interconnected to form solid crystals.

If the pressure had dropped during crystallization, the carbon atoms would have happily flattened into the lower energy atomic arrangement of graphite. (Graphite's carbons bond strongly to three others to form flat “chicken-wire” sheets that are in turn weakly bonded together in stacks. This is why we can write with graphite—rubbing your pencil tip across paper tears some of these weak bonds.)

When diamond traveled to the surface of the Earth, it did so explosively, in formations called kimberlite, carrot-shaped dry volcanoes originating in the mantle. Because the pressure on the diamonds in the mantle was released almost instantly, they were frozen in their higher energy state.

The Big Squeeze

Since Lavoisier's experiment, scientists have been searching for ways to convert graphite to diamond. The feat was finally accomplished by General Electric scientist Tracy Hall. He had developed a chamber called the “Belt Apparatus” because a belt runs around its outside to help contain the more than a million pounds per square inch (more than 69,000 kg per square cm) pressure the device is capable of withstanding.

On a wintry morning in 1954, after running his device at 70,000 atmospheres of pressure and 1,600 degrees C, he cracked open the chamber. “My eyes had caught the sparkling from dozens of tiny octahedral crystals…and I knew that diamond had been made by Man!” he wrote in a memoir. He scratched some sapphire with them, burned them in oxygen, and ran several other tests to prove his success. More than 150 tons of industrial diamonds—not to mention blue diamonds for some of the scientists' wives and green stones that were made into pins for the scientists themselves—have been manufactured in the “Belt.”

Just to prove that anything rich in carbon can be turned into diamond, another scientist at GE, Bob Wentorf, squeezed crunchy peanut butter (crunchy was his personal favorite), roofing tar, wood, and moth flakes into diamonds.

Since that fateful day, the science of diamond creation has exploded like kimberlite volcanic pipes. Today, its synthesis is modeled not only after nature's earthly diamonds: Another method mimics how diamonds formed in space. (Yes, space! One scientist estimates that there are a million trillion trillion trillion carats of diamond dust scattered around the Milky Way!)

Flawless diamonds can form in a vacuum, even with the pressure near zero, when carbon is heated to high enough temperatures that it forms a gas of single atoms. Crystallization into diamond is accomplished by controlling the conditions in the reaction vessel during cooling. Very large diamonds, even purer than nature's, have been made by this process, called chemical vapor deposition, or CVD.

In the laboratory of Yogesh Vohra at the University of Alabama at Birmingham, diamonds containing microcircuits are being synthesized. “Designer diamond anvils” are created when two of these are placed, tip to tip, in a high-pressure chamber. Various materials can then be squeezed between the diamonds at megabar (a megabar is one million times the Earth's atmospheric pressure at sea level) pressures, with the embedded microcircuits used to control temperature or take measurements. These are used to study how materials behave under very high pressures.

Speaking of chemistry, have you ever stopped to think about what the human body is made of? We are 23 percent carbon. A child weighing 80 pounds (36 kilograms) would have enough carbon to make 450 pencils or 41,400 carats of diamond. And how about this for gross: There is a company, LifeGem, which—for a high price—will make diamonds from the cremated remains of a loved one or a special pet. Diamonds really are forever.

Activity

A carat is a measurement of weight equal to .2 grams. What is the weight, in grams, of the 7.28 carat diamond found by a visitor to Crater of Diamonds State Park?[anno: The weight of this diamond was 1.456 grams.]

A diamond is made up of which element?[anno: A diamond is made up of carbon.]

In addition to some form of this element, what two things are necessary to create a diamond in a laboratory? Why?[anno: Answers should include that high pressure and high temperature are necessary to create a diamond in a laboratory because these conditions force the carbon atoms to crystallize. Then those crystallized carbon atoms are forced into the densely packed arrangement of a diamond.]